11/3/71 AS (I)
NAME as -- assembler
SYNOPSIS as name ...
1
DESCRIPTION as assembles the concatenation of name , .... as
1
is based on the DEC-provided assembler PAL-11R
[references], although it was coded locally.
Therefore, only the differences will be recorded.
Character changes are:
for use
@ *
# $
; /
In as, the character ";" is a logical new line;
several operations may appear on one line if sep-
arated by ";". Several new expression operators
have been provided:
\> right shift (logical)
\< left shift
* multiplication
\/ division
% remainder (no longer means "register")
! one's complement
[] parentheses for grouping
^ result has value of left, type of right
For example location 0 (relocatable) can be writ-
ten "0^."; another way to denote register 2 is
"2^r0".
All of the preceding operators are binary; if a
left operand is missing, it is taken to be 0.
The "!" operator adds its left operand to the
one's complement of its right operand.
There is a conditional assembly operation code
different from that of PAL-11R (whose condition-
als are not provided):
.if expression
...
.endif
If the expression evaluates to non-zero, the sec-
tion of code between the ".if" and the ".endif"
is assembled; otherwise it is ignored. ".if"s
may be nested.
Temporary labels like those introduced by Knuth
[references] may be employed. A temporary label
is defined as follows:
n:
where n is a digit 0 ... 9. Symbols of the form
"nf" refer to the first label "n:" following the
use of the symbol; those of the form "nb" refer
to the last "n:". The same "n" may be used many
times. Labels of this form are less taxing both
on the imagination of the programmer and on the
symbol table space of the assembler.
The PAL-11R opcodes ".word", ".eot" and ".end"
are redundant and are omitted.
The symbols
r0 ... r5
sp
pc
ac
mq
div
mul
lsh
ash
nor
csw
..
are predefined with appropriate values. The sym-
bol "csw" refers to the console switches. ".."
is the relocation constant and is added to each
relocatable symbol. normally it is 40000(8); it
may be changed to assemble a section of code at a
location different from that in which it will be
executed.
It is illegal to assign a value to "." less than
its current value.
The new opcode "sys" is used to specify system
calls. Names for system calls are predefined.
See the section on system calls for their names.
Strings of characters may be assembled in a way
more convenient than PAL-11's ".ascii" operation
(which is, therefore, omitted). Strings are in-
cluded between the string quotes "<" and ">":
<here is a string>
Escape sequences exist to enter non graphic and
other difficult characters. These sequences are
also effective in single and double character
constants introduced by single (') and double (")
quotes respectively.
use for
\n newline (012)
\0 NULL (000)
\> >
\t TAB (011)
\\ \
The binary output of the assembler is placed on
the file "a.out" in the current directory. a.out
also contains the symbol table from the assembly
and relocation bits. The output of the assembler
is executable immediately if the assembly was
error-free and if there were no unresolved exter-
nal references. The link editor ld may be used
to combine several assembly outputs and resolve
global symbols.
The multiple location counter feature of PAL11R
is not supported.
The assembler does not produce a listing of the
source program. This is not a serious drawback;
the debugger db discussed below is sufficiently
powerful to render a printed octal translation of
the source unnecessary.
FILES /etc/as2 pass 2 of the assembler
a.tmp1 temporary
a.tmp2 temporary
a.tmp3 temporary
a.out object
SEE ALSO ld, nm, sh, un, db, a.out (format of output)
DIAGNOSTICS When an input file cannot be read, its name fol-
lowed by a question mark is typed and assembly
ceases.
When syntactic or semantic errors occur, a
single-character diagnostic is typed out together
with the line number and the file name in which
it occurred. Errors in pass 1 cause cancellation
of pass 2. The possible errors are:
) parentheses error
] parentheses error
* Indirection ("*") used illegally
A error in Address
B Branch instruction has too remote an ad-
dress
E error in Expression
F error in local ("F" or "b") type symbol
G Garbage (unknown) character
M Multiply defined symbol as label
O Odd-- word quantity assembled at odd ad-
dress
P Phase error-- "." different in pass 2 from
pass 1 value
R Relocation error
U Undefined symbol
X syntaX error
BUGS Symbol table overflow is not checked.
OWNER dmr